In general the present invention relates to telephone station equipment, and more particularly to multiple telephone set installations serviced by multiple telephone lines from a central office.
Many telephone customers, especially businesses, need a telephone installation in which calls can be placed or received at any one of a number of telephone sets, and over any one of a plurality of available telephone lines from a central office. Such installations are in general available and are called key telephone systems (or KTS). One of the most commonly used systems of this type is intended for meeting the needs of customers that require a relatively large number of telephone lines, such as five or more lines, and for these customers the cost of the service is not unreasonable on a per line basis. However, there is a need for a less complex, lower cost key telephone system capable of efficiently meeting the needs of customers that have phone traffic requiring less than five lines but more than one line. For example, it is believed that there are many customers, in small businesses for example, that have a definite need for two line, key telephone service, but cannot justify the cost of such service because most available key telephone systems are cost efficient when used with five or more telephone lines.
One of the reasons for the prohibitively high cost of key telephone systems when used for two line installations is that the system includes a central control unit that must be set up and stored at a location remote from the telephone sets. The central control unit in turn involves a substantial installation cost, both for the control unit itself and also for the auxiliary wiring that must be strung between the control unit and each of the multiple telephone sets. Also, the telephone sets themselves must be specially made to accommodate the maximum number of key functions for which the system has been designed. For example, a standard KTS desk set may provide for five or more line select buttons, even though the customer is only using the system for two lines and thus only two of the available buttons are functional.
Although other telephone systems are available for providing a form of two line service on a relatively low cost basis, none of these existing two line systems have the capability or offer the convenience and flexibility of key telephone systems.
Accordingly, it is an object of the invention to provide a novel low cost key telephone system that is particularly tailored for customers needing less than five telephone lines from a central office.
Another object is to provide such a key telephone system on which the control circuitry, visual indicator lights and manual control buttons for each telephone station are capable of being packaged in a small, compact unit that is readily attachable to an existing, standard telephone desk set of the type intended for single line use.
Another object is to provide such a key telephone system having a conference call capability.
Another object is to provide a key telephone system that eliminates the need for a central control unit and the attendant disadvantages thereof including the loss of office or storage space otherwise needed for the central control unit and the high labor cost entailed in installing wiring between the control unit and the various telephone sets.
A further object is to provide a key telephone system which uses supervisory signals applied to the telephone lines by the central office to display the operating conditions of the lines at each set.
Additionally, it is an object of the invention to provide a key telephone system that has one or more of the foregoing advantages and is capable of being manufactured at a relatively low cost per unit, and is durable, operationally reliable, easily serviceable, and compatible with existing central office equipment and signalling.